1. Field
This application relates to an envelope tracking current bias circuit and a power amplifier apparatus that may be applied to a communications system.
2. Description of Related Art
In general, power amplifier modules (PAMs) amplify radio frequency (RF) signals in transmitters and transmit the amplified RF signals to antennas. Because such PAMs support a wide range of frequency bands, the PAMs may include a plurality of switches, a plurality of filters, and a plurality of power amplifiers (PAs) amplifying RF signals.
The performance of PAMs may be evaluated by maximum output, efficiency, linearity, and other performance measures. PAMs are components that use a relatively large amount of current in mobile phones, and accordingly current consumption may be also one of the performance measures of PAMs.
Envelope tracking (ET) is used as one method for reducing the current consumption of PAMs. ET allows the power supply voltages of PAs to vary depending on the envelopes of RF signals. That is, when the power of RF signals is low, the magnitude of the power supply voltages of PAs is reduced to decrease the average current consumption of PAMs. Conversely, when the power of RF signals is high, the magnitude of the power supply voltages of PAs is increased to prevent the linearity of PAMs from deteriorating.
To increase efficiency by reducing current consumption, one example of a PAM in the related art appropriately processes shaped envelope signals using envelope tracking modules (ETMs) or envelope trackers (ETs), and uses the processed shaped envelope signals as the power supply voltages (VCC or VCC_PA) of PAs.
However, such PAMs in the related art have not provided a scheme for efficiently supplying a bias current to further reduce current consumption.
Other PAMs in the related art set a power supply voltage VCC to vary in response to the envelopes of RF signals, and set a bias current at a fixed value predetermined according to a preset table value.
However, since such PAMs set a bias current as a fixed value and provide a relatively high level of bias current to provide biasing without deterioration, even in a case in which the power of RF signals is high, the PAMs provide a higher level of bias current than necessary in a case in which the power of RF signals is low, causing a relatively high level of current consumption.
In a case in which PAMs in the related art supply power supply voltages based on envelopes while using a fixed bias current, the supply power supply voltages may be coupled to input signals in the opposite phase of the output signals of PAs. In this case, degradation of amplitude modulation-phase modulation (AM-PM) distortion characteristics of the PAMs may cause deterioration of adjacent channel power ratio (ACPR) performance of the PAMs.